Measured Business Line (MBL)

Nsight Business Voice—MBL More Than a Plain Old Telephone Service

It’s a critical interaction with your customers.

Plain old telephone service [originally “Post Office Telephone Service/System” (POTS)] is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world.

The name is a retronym, and is a reflection of the telephone service still available after the advent of more advanced forms of telephony such as ISDN, mobile phones and VoIP. POTS has been available almost since the introduction of the public telephone system in the late 19th century in a form mostly unchanged to the normal user despite the introduction of Touch-Tone dialing, electronic telephone exchanges and fiber-optic communication into the public switched telephone network (PSTN).

The system was originally known as the Post Office Telephone Service/System in many countries. The term was dropped as telephone services were removed from the control of national post offices.

POTS includes:

  • bi-directional, or full duplex, voiceband path with limited frequency range of 300 to 3400 Hz. In other words, a signal to carry the sound of the human voice both ways at once;
  • call-progress tones, such as dial tone and ringing signal;
  • subscriber dialing;
  • operator services, such as directory assistance, long distance calling, and conference calling assistance;
  • a standards-compliant analog telephone interface including BORSCHT functions

In the United States and Australia, the pair of wires (RJ25 Connector in Australia) from the central switch office to a subscriber’s home is called a subscriber loop. It is typically powered by −48V direct current (DC) and backed up by a large bank of batteries (connected in series) and in some cases, an additional electric generator in the local exchange, resulting in continuation of service during most commercial power outages. The subscriber loop typically carries a “load” of about 300 ohms, and does not pose a threat of electrocution to human beings (although shorting the loop can be felt as an unpleasant sensation).

Many calling features became available to POTS subscribers after computerization of telephone exchanges during the 1970s and 1980s. The services include:

  • Voicemail
  • Caller ID
  • Call waiting
  • Speed dialing
  • Conference call (three-way calling)
  • Enhanced 911
  • Centrex

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